Heat-treated zirconium steel and process of making same



creased hardness,

Patented Aug. 18, 1925.

UNITED STATES PATENT OFFICE.

FREDERICK M. BECKETAND ALEXANDER L. FEILD, NEW YORK, -Y., ASSIGNOCES TOELECTED METALLURGICAL COMP- NY. A CORPORATION OF WEST VIRGINIA.

I HEAT-TREATED ZIRCONIUM STEEL AND PROCESS OF MAKING- SAME.

1% Drawing.

To all whom it may concern:

Be it known that we, FREDERICK M. BECKET and ALEXANDER L. FEILD,citizens of the United States of America, residing at 565 Park Ave, and52 East 41st Street, respectively, New York, in the county of New Yorkand State of New York, have invented.- certain new and usefulImprovements in Heat-Treated Zirconium Steel and Processes of. MakingSame, of which the following is a specification.

This invention relates manufacture and comprises a process forheat-treating steel containing zirconium whereby is obtained a productpossessing mechanical properties of a superior order of.merit. Theinvention comprises also, as a novel product, a heat-treated steel,sin1i lar in composition to an ordinary carbon steel except for thepresence therein'of a small percentage-of zirconium, (with or withoutsmall percentages of certain other alloying elements as hereinafter morefully described) yet which possesses properties hitherto obtainable onlyin the so-called alloy steels containing in customary amount (that is tosay, the sum of the alloying elements usually upward-of one per cent)one,

or more of the well known alloying elements such as chromium, nickel,vanadium, and molybdenum. These results are attained, in accordance withthe present invention, by

the heat-treatment of a steel having a zir-' conium content, saidzirconium being incorporated in the molten steel bath during the rocessof manufacture. Optimum treating conditions in so far as now known arehereinafter set forth.

As is Well known, it is possible by the heat-treatment of steels of thegrades known as forging, tool, or spring steels to obtain productspossessing a wide range of properties. Generally speaking, the higherthe temperature employed I to dl aw or temper a given quenched steel,the greater is the ex tent to which the initial properties of thequenched steel are altered in the direction of increased ductility andtoughness, de-

and lowered tensile strength. In the manufacture of heat- .treatedforgingsand rolled products a temporing or drawing temperature iscommonly employed whichresults in'such balancing of the variousmechanical properties as appears, from practical experience and thetothe art of steel Application filed January 25, 1923. Serial No. 615,438.

oretical considerations, to be most desirable and advantageous from thestandpoint of serviceability or engineering design, or both. In theautomobile and air-craft industries, in particular, the propertiesobtainable by the employment of the various commercial alloy steels inthe heat-treated state have been especially desirable, due among otherthings, to the obvious advantages of decreased weight and the ability ofsuch steels to Withstand severe service conditions.

We have found it possible, in accordance with the present invention, soto improve the properties of an ordinary carbon steel by theincorporation therein of a small percentage of zirconium followed bysuitable heat-treatment that the resulting heattreated product hasproperties much more nearlycomparable to those of the more 8X pensiveheat-treated alloy steels to which reference has'already been made.

The effect of zirconium, employed under conditions as specified below,is exhibited in a tendency to maintain the ductility of the steels, asindicated by per cent reduction '350450 C. The desired effect is broughtabout in marked degree by the presence in the steel, for instance, ofabout 0.15 per cent zirconium in the case of a steel of about 0.70 percent carbon content. As a preferred range of zirconium content we wouldspecify from 0.04 to 0.40 per cent zirconium, although we do notconsider the present invention to be restricted to any particular rangeofcontained zirconium.

There exist -a multiplicity of methods, familiarto those skilled in-theart, bywhich the zirconium may be incorporated in the molten steel. Itis preferably added to the steel (for example in the furnace or ladle),in the form of an alloy with silicon, or in the form of an alloy oraggregate containing zirconium and silicon. But our invention is notlimited to the use of zirconium in conjunction with silicon, or to itsintroduction in the form of an alloy.

The table which follows contains under columns I and II the results oftests con ducted on two steels tapped from the same electric furnaceheat. The steels analyzed 0.70 per cent carbon, 0.62 per cent manganese,0.026 per cent phosphorus, and 0.03 per cent 5 sulphur. They wereidentical in com sition and manner of treatment except that the steeldescribed under column I contained 0.15% zirconium, incorporated in themolten steel in the form of an alloy of iron, silicon 1 and zirconium,(ferrosilicon-zirconium).

Columns I and II contain the results obtained' b drawing, at fivedifferent tem era tures, t e steels previously quenche in water from 825C. The zirconium-treated 1 and the untreated steels were, for eachtemerature of draw, heat-treated simultaneousiy and with everyprecaution to secure uniformity of pract ce to the end that the testdata might be strictly comparable. M

TABLE 0.70% carbon without zirconlum Drawing temperature Per centelongation $0 Per cent reduction claret..- Yield point, lbs. sq. inUltimate strength, lbs. sq. in-

Izod number, lt.-1bs. Brinell hardness Drawing temperature", Per centelongation Per cent reduction of area. Yield point, lbs. sq. in Ultimatestrength lbs. sq. in- Izod number, tt.-lbs v Brinell hardness Drawingtemperature....

Per cent elongation Brinell hardness Drawing temperature Per centelongation Per cent reduction 0! area.. Yield point, lbs. sq. inUltimate strength, lbs. sq. in Izod number, it.-lbs Brlnell numberDrawing tem tnre.....

Per cent elongation.

The Izod numbers given under columns I and-II were obtained by testsconductedwith 5 a 120 ft-lb. Izod machine, using a testpiece of 10 b 10mm cross-section, a 2-mm. 45 notch with 0.01 inch radius at' the bot:tom, and a'striking distance of 0.866 inches.

The notch was out after the test pieces were heat-treated." .Itiwill beaarent to those familiar with this art that t e properties-of thezirconiumtreated steel, as given in column I, closely approach those 0certain alloy steels. For convenience of comparison we have given in,quenched steels during the temperingiproc- The Izod numbers for thesteel of column III are not available. It is, however, certainly truethat the'zirconium-treatedsteel above described has a value fornotch-toughness (Izod number) which falls not far below that of anickel-vanadium or chromevanadium steel tempered to produceapproximately the same ultimate strength and duetility 1 We have alsoconducted comparative experiments onheat-treated carbon steelscontaining both more and' less than 0.7 0 per cent of carbon, with andwithout a zirconium content, and have found beneficial effects due tozirconium similar to those above de scribed. We conclude therefore thatour discovery is applicable broadly to the heattreatment of carbonsteels containing zirconium.

The most notable improvement brought about by zi'rconiumoccurs, as canbe seen,

in that range of drawing temperatures associatedwith the formation oftroostite in the finished product, 350450 C.

. An advantageous manner of practicing the invention is to draw(ltemper) the steel in a furnace, for examp e of the electric 0 muiiletype, in such manner thatthe heattreated parts are'brought u to thetemperature of the furnace by re. iation from the walls, and thereafterallowed to remain at this temperature for an appreciable period,

say 15 minutes for a standard testpiece;

then remove and allow to cool in air. Suchtreatment has given decidedlybetter results both in the zirconium-treated and themtreated (control)steel than a 15-minute draw in a lead bath at correspondingtemperatures. Evidently the rate of heating during the draw, or the timeof draw, or both, have an important efl'ect upon the transformationsoccurring in the steel. Just what is the exact optimum procedure,however, is a'question which must be determined for each kind and gradeof steel b means of a simple series of tests ofthe c aracter usuallyapplied for this purpose.

, The structural changes occurring in ess are not yet fully understood.the

'- present state of knowledge relating. to this narrower range oftemperature than is possible in steel not contalning zirconium, and

probably before the appearance of an appreciable amount of sorbite.

There are a large number of chemical elements which if present in steelsin sufficient quantity, either singly or in combination, give rise tocompositions which are technically known as alloy steels. It will beunderstood that steels as produced industrially are rarely if everentirely free from all these elements. Certain of the alloying elements,for example silicon and manganese, are normal constituents of carbonsteels as now made, but the quantities present in such carbon steels areinsufiicient to produce the characteristic alloy steels of theseelements. Most or all of the other alloying elements are at timespresent in small quantities in steels which are nevertheless universallydesignated as carbon steels. In many cases such elements are introducedfortuitously, it being impracticable to exclude them completely from theraw materials, including steel scrap, which make up the furnace charge.

VVeregarcl as within the scope of our invention all heat-treated steelscontaining zirconium and containing other alloying elements in less thantheir normal alloying proportions when such steels are characterized bysubstantially higher ductility than is characteristic of zirconium-freesteels of comparable composition, strength, and hardness; and we make noexception to. the foregoing when the alloying element or elements (otherthan zirconium) are intentionally added to produce a special efiect.

We claim:

1. A heat-treated carbon steel containing zirconium and characterized bysubstantially higher ductility as indicated by percent reduction of areathan is characteristic of zirconium-free steels of comparable strengthand hardness.

2. A heat-treated carbon steel containing 0.0i..to' 0.40 per centzirconium and characterized by substantially higher ductility asindicated by per cent reduction of area than is characteristic ofzirconium-free steels of comparable strength and hardness.

3. Heat-treated steel containing zirconium in association with analloying element or elements, the latter in less than normal alloyingproportion.

4. Heat-treated steel containing 0.04 to 0. .0 per cent zirconium inassociation with an alloying element or elements, the latter in lessthan normal alloying proportion.

5. The herein described process comprising introducing zirconium into acarbon steel, and heat-treating the product, whereby it acquires asubstantially higher duc tility as indicated by per cent reduction ofarea than is characteristic of zirconiumfree carbon steels of comparablestrength and hardness.

6. The herein described process comprising introducing 0.04 to 0.40 percent zirconium into a carbon steel, and heat-treating the product,whereby it acquires a substantially higher ductility as indicated by percent reduction of area than is characteristic of zirconiunrfree carbonsteels of comparable strength and hardness.

7 The herein described process comprising introducing into a steelzirconium and an alloying element or elements, the latter in less thannormal alloying proportion, and

-heat-treating the product.

8. The herein described process comprising introducing into a steel0.04. to 0.40 per cent zirconium and an alloying element or elements,the latter in less than normal alloying proportion, and heat-treatingthe product.

In testimony whereof, we aiiix our signatures.

FREDERICK M. BECKET. ALEXANDER L. FEILD.

